1. Field of the Invention
The present invention relates to an abrasive pad preferably used for chemical-mechanical polishing (CMP) in order to make a mirror surface finish and to preferentially abrade a convex portion of irregularities on a surface of a working piece. The surface of the working piece is abraded by pressing the working piece against a rotating elastic pad, and allowing a relative motion while supplying an abrasive solution that contains processing abrasive grains or an abrasive solution that contains no abrasive grains.
2. Description of the Related Art
In order to realize multi-layer interconnection for producing a highly integrated semiconductor, it is necessary to completely flatten the surface of an insulated film. As typical technologies for this flattening method, an SOG (Spin-On-Glass) method, etchback method, lift-off method and the like have been investigated.
As regards the SOG method, which is a flattening method utilizing the fluidity of an SOG film, it is impossible to attain complete flattening by this method alone. The etchback method is a most widespread technique; however, a problem arises in that dust is generated by simultaneous etching of a resist and an insulated film and hence dust control is not easy. The lift-off method has a problem in that lift-off cannot be attained since stencil materials to be used are not thoroughly soluble at the time of lift-off, and therefore the method is still beyond practical use due to insufficient controllability and yield.
Under the above circumstances, a chemical-mechanical polishing method (CMP method) is recently attracting attention. In this method, the convex portion of irregularities on the surface of the working piece is preferentially abraded by pressing the working piece against a rotating elastic pad and allowing a relative motion, and is currently widely used due to simplicity of the process.
In recent years, a problem has arisen concerning surface defects, especially surface defects caused by minute irregularities associated with a pre-processing semiconductor wafer, relating to a term “nano-topology” and is a current issue. In order to cope with the problem, double-sided surface abrasion, a method of abrading substance surfaces while flowing an alkali, or the like are carried out.
Such a CMP method, however, poses problems of scratching, dust adhesion, and global flatness inferiority occurring on the surface of materials to be abraded. If dust adhesion and scratching occur on the surface of, for example, an intra-layer insulating film to be abraded, a stepping phenomenon or the like may occur when forming wiring of, for example, an Al or Cu type metal on the abraded layer in a subsequent step, possibly leading to reduced reliability such as deteriorated electro-migration durability. Also, loss of regenerative signals may be caused such as dropouts in abrasion of nonmagnetic base materials for HDDs (Hard Disk Drive). Scratching are thought to be caused by aggregated particles that have failed to disperse. Especially, an abrasive slurry produced by adopting alumina as abrasive particles and used for metal layer CMP has poor dispersibility and is unsatisfactory in preventing scratching. The cause of dust adhesion is not yet clearly understood. Generally, a hard abrasive pad is used to improve global flatness, but incidences of dust adhesion and scratching may easily occur, and hence is not considered to meet both of the two desired characteristics mentioned above.
In order to improve global flatness and reduce dust adhesion and scratching, several techniques have been proposed (see, for example, Japanese Patent Application National Publication (Laid-Open) No. 8-500622 and Japanese Patent Application Laid-Open (JP-A) No. 2000-34416). These techniques, however, have not attained both characteristics of dust adhesion/scratching and flatness.
In order to attain effective flattening by employing CMP or other abrasive methods, the transfer and dispersion of a slurry onto the surface to be abraded are important. When a large number of abrasive methods, in particular, abrasive methods requiring high rotational speed and pressure are employed, insufficient fluidity of the slurry contained in an abrasive pad may lead to a ununiformly abraded amount per hour, and thus resulting in inferior surface qualities of base materials or deteriorated quality of the abrasive pad. In view of the foregoing, various efforts have been made to improve the transfer of the slurry. For instance, Cook et al. have proposed use of a large- or small-sized flow pass to facilitate the transfer of the slurry to the entire surface area of a hard abrasive pad (see, for example, U.S. Pat. No. 5,489,233), and Shamouillian et al. disclose an abrasive pad that is designed to make an abrasive slurry more fluidic by providing a flow pass through at least a part of the abrasive pad (see, for example, U.S. Pat. No. 5,533,923). Breivogel et al. have also proposed an abrasive pad provided with holes arranged at regular intervals for conveying the slurry to the entire surface of the pad (see, for example, U.S. Pat. No. 5,554,064).
In spite of these attempts, excellent characteristics with respect to dust adhesion/scratching and flatness have not yet been attained. In order to achieve both of these desired characteristics, good wettability of the surface sufficient to make the slurry readily conveyed to the surface to be abraded, as well as hydrophilic passes to allow the slurry to be easily supplied to an inside of the abrasive pad should be ensured. However, a pad that attains these characteristics has not yet been developed.